Volcano‐Shaped Carbon Capacitive Sensor for Synergistic Monitoring and Reinforcement of Adhesive Layer in Composite T‐Joints

ABSTRACT Carbon fiber reinforced plastic (CFRP) T‐joints are widely used in aerospace structures, and the curing quality and peel resistance of their adhesive layer remain challenging. Herein, a novel carbon nanotube (CNT) capacitive sensor is proposed to in situ monitor and mechanically reinforce the adhesive layer of CFRP T‐joints. CNT sensors with volcano‐shaped convex holes (CHs), planar holes (PHs), and non‐holes (NHs) were prepared and integrated into the adhesive layer of CFRP T‐joints. The results show that CNT sensors possess stable capacitance signals and low signal‐to‐noise ratios. During the curing process, the capacitance change (Δ C / C ₀ ) versus time curves of specimens containing CNT sensors exhibit a unimodal characteristic. Compared with the specimens containing PH and NH, the maximum Δ C / C ₀ of specimens containing CH increases by 82% and 66%, respectively. Meanwhile, the maximum Δ C / C ₀ increases with increasing pressure or temperature. Moreover, during the peel testing, compared with specimens containing PH and NH, the average Δ C / C ₀ of specimens with CH respectively increases by 112% and 194% at damage initiation. The ultimate load of T‐joints containing CH, PH, and NH, respectively increases by 13.03%, 2.8%, and −5.7% compared with the base T‐joint. Therefore, the CH capacitive sensor with volcano‐shaped array holes shows advantages of structural‐functional integration.